The invention relates to a steering gear, and in particular to a steering gear for a power steering system of a motor vehicle.
In most motor vehicles, there are installed power steering systems which, during steering maneuvers, generate an assisting moment and thereby reduce the steering moment that has to be imparted to the steering column by the driver.
Known power steering systems are based on a steering gear which converts the drive power of a hydraulic or electric drive and transmits said drive power to the steering column. Steering gears of said type are generally in the form of a helical rolling-type gear, and are in particular in the form of a helical wheel gear or pinion gear, that is to say said steering gears comprise a gearwheel, which is connected directly or indirectly to the steering column, and a pinion which is driven by the drive via a pinion shaft.
In the case of such steering gears, gearing play has proven to be a problem, said gearing play arising owing to component tolerances, different thermal expansion of the gearing elements and wear. In particular during so-called alternating steering, that is to say during directly successive steering maneuvers with alternating steer angle, such gearing play generates undesired noises resulting from alternating abutment of opposite flanks of teeth of the pinion and gearwheel.
It is known for said gearing play to be eliminated by virtue of the pinion shaft being mounted so as to be pivotable about an axis running perpendicular to the longitudinal axis of the pinion shaft and at a distance from the toothing engagement of pinion and gearwheel, and being pressed against the gearwheel by means of one or sore spring elements. Here, the pivoting capability of the pinion shaft is integrated into one of the two bearing arrangements by which the pinion shaft is mounted at its ends. Said bearing arrangement is also referred to as “fixed bearing”. The bearing arrangement in the region of the other end is then implemented with play (so-called “floating bearing”) in order to permit the deflection caused by the pivoting movement. The fixed bearing is generally provided at the drive side, whereas the floating bearing is provided on the free end of the pinion shaft. The one or more spring elements for pressing the pinion against the gearwheel are generally integrated into the floating bearing.
A corresponding generic steering system is known for example from WO 2011/073089 A1. In said document, provision is made for the rolling bearing which receives the pinion shaft in the region of the fixed bearing to be mounted, at the outside, in a pivot ring. The pivot ring comprises an inner ring, which receives the rolling bearing substantially without play, and an outer ring, which is held substantially without play in a bore of a housing of the steering gear, wherein the outer ring and the inner ring are connected by way of multiple narrow webs which are twisted in the event of a rotation of the outer ring relative to the inner ring.
Other solutions for forming the pivotable fixed bearing provide for the rolling bearing to be pivotably mounted, at the outside, in a plain bearing or, at the inside, in a silent bushing, or simply for a rolling bearing to be provided which has such a degree of play that the desired pivoting capability can be realized.
In the known solutions, owing to the construction, the pivot axis intersects the central axis of the fixed bearing, or the longitudinal axis of the pinion shaft.
A disadvantage of the bearing arrangements known from the prior art for realizing freedom from play in the engagement between pinion and gearwheel is the fact that there is noticeably different steering behavior during anticlockwise and clockwise rotation of the steering column.